The invention relates to a method for checking the conversion capacity of a catalytic element for clearing ozone which is present in a vehicle.
For reasons of environmental and personal protection, the levels of pollutants which result from vehicles with an internal combustion engine or from the generation of energy using stationary combustion installations need to be significantly reduced.
A novel approach to reducing the levels of pollutants consists in actively removing pollutants not directly from the exhaust-gas stream from an internal combustion engine or a stationary combustion installation, but rather from the ambient air. This route is promising in particular for the removal of ground-level ozone, which has a considerable influence on the well-being of people on account of its strongly oxidizing action. Ozone itself is not a gas which is emitted directly and therefore cannot be removed in the exhaust-gas stream. It is formed when nitrogen oxides are present in outside air under solar radiation, on account of the UV component of this radiation, through complex photochemical reaction equilibria.
Since ozone is extremely reactive, it can easily be broken down quantitatively by means of a catalyst system through which air flows. These catalysts are extremely stable, since there is no need for any direct action of strong oxidation catalysts, which are highly sensitive to poisoning, such as for example platinum. Systems which substantially effect adsorption of the ozone on a surface are sufficient; this ozone then breaks down instantaneously to form oxygen.
Catalyst systems of this type have long been in use in passenger aircraft which fly close to the ozone layer, where they are used to treat the air which is passed into the passenger compartment. Recently, such systems have also been deployed in motor vehicles. Here, the radiator of the vehicle is coated with the catalyst. The large quantities of air flowing through the radiator are quantitatively cleaned of ozone, i.e. the vehicle cleans the ambient air.
When ozone catalyst systems of this type are used, the American environmental agency CARB (California Air Resources Board) grants automobile manufacturers a bonus (credits) with regard to the exhaust-gas limits for the LEV (Low Emission Vehicle) exhaust legislation. However, the credits are only granted if there is on-board diagnosis of the ozone catalyst system.
A system of this type is described in SAE Paper 2001-01-1302xe2x80x9cPremAir(copyright) Catalyst Systemxe2x80x94OBD Conceptsxe2x80x9d, Ronald M. Heck, Fred M. Allen, Jeffrey B. Hoke and Xiaolin Yang; Engelhard Corporation.
The invention is based on the object of providing a method for checking a catalyst which is used for ozone conversion in a vehicle. The object is achieved in accordance with the features of the invention in the patent claims.
The method according to the invention is distinguished by the fact that, to check the conversion capacity of a catalytic element for cleaving ozone, which is arranged in a vehicle and is exposed to an ambient-air stream, a first ozone sensor is arranged upstream of the catalytic element in the ambient-air stream, in order to record the ozone concentration prevailing at that location, and a second ozone sensor is arranged downstream of the catalytic element in the ambient-air stream, in order to record the ozone concentration prevailing at that location. The check is only carried out if predetermined enable conditions are satisfied. Only in this case are the values emitted by the sensors recorded and compared with one another. A variable which represents an uncorrected value for the quality of the conversion capacity is derived from this comparison. Then, this variable is weighted as a function of at least one operating parameter of the vehicle. The weighted variable is compared with a predetermined threshold value and, if the threshold value is exceeded, it is concluded that the conversion capacity of the catalytic element is insufficient.